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Joining Metals
Selection of Joining Metals
Brazing is the most efficient metal joining process. It produces bonds,
which are stronger than the metals joined. The metals to be joined are
called base metals. The metals to be joined can be same or different. The
most frequent base metals are copper, nickel, silver, aluminum, gold, etc.
Not only pure metals are joined by the brazing, their alloys are used as
well.
1) Aluminum & Aluminum Alloys
A number of variations of aluminium and their alloys are used for brazing.
The most commonly brazed alloys are given in the table below. Those
aluminium alloys, which contain higher percentage of Mg are more difficult
to braze because of poor wetting by filler metal and excessive penetration.
| Aluminum Alloys |
| Al 0.25% Cu 0.6% Si 1.0% Mg 0.25% Cr |
Al 0.25% Cu 0.35% Si 0.6% Mg 0.25% Cr |
| Al 1% Zn |
Al 1.2% Mn |
2) Copper & Copper Alloys
Copper and its alloys are readily joined by the brazing processes. Oxygen
containing coppers are not usually fit for brazing owing to loss of
ductility and strength, and due to oxide migration. Atmosphere containing
hydrogen also embrittles this material. However oxygen free copper is widely
used and suitable for brazing components.
| Copper Alloys |
Comments |
| Cu-Zn alloys |
The loss of zinc should be minimized by fluxing the components
because it results in reduction of hardness and tensile strength. |
| Cu-Si alloys |
These alloys should be stress relieved because in stressed
condition they are prone to inter-granular penetration of filler metal
with a continuous loss in mechanical properties. |
| Cu-Al alloys |
Special fluxes are required for brazing Cu-Al alloys because
refractory aluminum oxides are formed at brazing temperature. |
| Cu-Be alloys |
For brazing copper-beryllium alloys, silver brazing rods using flux
are employed. |
| Cu-Ni alloys |
Cu-Ni alloys are susceptible to inter-granular penetration and
cracking if stressed. It can be brazed readily with silver brazing rods.
|
| Cu-Sn alloys (Phosphor Bronze) |
These alloys may be brazed using silver, copper-phosphorus or
copper-zinc filler rods. |
3) Steels
| Steels |
Comments |
| Low Carbon and low alloy steels |
Low carbon steels are brazed with ease. Low alloy steels tend to
harden. It should be brazed below the critical temperature. |
| Stainless and heat-resisting steels |
Due to high Cr content, special fluxes are required for refractory
oxides and difficult wetting. Extra low carbon stainless steels or
stabilized (Ti or Nb) steels are suitable for brazing by the nickel
group fillers. |
4) Cast-Iron
Silver brazing filler rods are perfect for brazing malleable and ductile
cast-irons. The silver filler reduces the oxidation effect and make wetting
easier.
5) Nickel and Nickel Alloys
Traces of S, Pb, Bi or Sb make nickel and high nickel alloys prone to
embrittle. These alloys should be cleaned properly prior to brazing to
assure the removal of any substance containing them. The parts should be
stress relieved to avoid stress corrosion cracking.
6) Beryllium
Beryllium and its alloys has been brazed for use in missiles, nuclear
reactors and aircraft.
7) Other Brazeable Materials
- Ceramics
- Graphite
- W, Mo, Ta and Cb
- Carbides and cermets
- Gold, Platinum and Palladium.
- Titanium and zirconium base metals
- High carbon and high speed tool steels
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